1. Field of the Invention
This invention relates to sensors for electronic control of a vehicle powertrain.
2. Prior Art
Four wheel drive systems can use transfer cases to apply drive line power from an input shaft coupled from the transmission and engine to a rear drive shaft coupled to the rear wheels and to a front drive shaft coupled to the front wheels. Selecting whether power is applied to the rear drive shaft, the front drive shaft or to both drive shafts is a function of the absolute and relative speeds of the front and rear drive shafts and of processing done by a transfer case controller. Typically, sensors are coupled to the front and rear drive shafts to determine speed of rotation of the drive shafts. It is known to use various coupling gears to provide a fixed scaling ratio which can be used to convert the output signal of the sensor coupled to the drive shaft to indicate the speed of rotation of the associated wheels. Thus the transfer case controller assumes a fixed sensor calibration for all vehicles and uses a fixed sensor calibration constant.
However, the use of such coupling gears presents a problem because it increases the number of parts, and introduces the possibility of error by installation of the wrong part. Further, the particular gear ratio of the coupling gear is uniquely determined as a function of the vehicle and its driveline/powertrain configuration and thus must be appropriately matched.
It would be advantageous to have a system which automatically calibrates a sensor associated with the drive shafts to produce an indication of tire rotation or vehicle speed. These are some of the problems this invention overcomes.